Lock-up device for torque converter

ABSTRACT

A lock-up device transmits a torque through a turbine of a torque converter. The lock-up device includes a friction surface, a clutch disc, a piston and a pressure plate. The friction surface is provided on a lateral surface of a front cover. The clutch disc has an annular shape and is capable of being pressed in contact with the friction surface. The piston is disposed between the front cover and the turbine. The piston is movable in an axial direction. The pressure plate has an annular shape. The pressure plate is disposed between the piston and the clutch disc, and presses the clutch disc toward the front cover by a pressing force to be applied thereto from the piston. The pressure plate has a lower bending stiffness than the piston, and is deformable in accordance with deformation of the front cover when pressed toward the front cover by the piston.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase of PCT InternationalApplication No. PCT/JP2016/064793, filed on May 18, 2016. Thatapplication claims priority to Japanese Patent Application No.2015-102485, filed on May 20, 2015, Japanese Patent Application No.2015-102486, filed on May 20, 2015, Japanese Patent Application No.2015-102487, filed on May 20, 2015, and Japanese Patent Application No.2015-102488, filed on May 20, 2015. The contents of all fiveapplications are herein incorporated by reference in their entirety.

BACKGROUND Technical Field

The present disclosure relates to a lock-up device, and particularly toa lock-up device for a torque converter, which transmits a torque from afront cover to a transmission-side member through a turbine of thetorque converter.

Background Information

Torque converters are often equipped with a lock-up device that directlytransmits a torque from a front cover to a turbine. The lock-up deviceincludes a clutch part disposed between the front cover and the turbineand a damper disposed between the clutch part and the turbine. The frontcover includes a friction surface on a surface thereof opposed to theclutch part, whereas the clutch part includes, for instance, a pistonthat a friction member is fixed to a lateral surface of the outerperipheral part thereof. Additionally, the piston is axially moved bythe pressure of hydraulic oil, and the friction member is pressed incontact with the friction surface of the front cover, whereby a lock-upon state (a power transmission activated state) is made.

Here, the hydraulic oil is supplied to the interior of the torqueconverter during actuation of the torque converter. Hence, the internalpressure of the torque converter increases. Chances are that the frontcover is deformed by increase in internal pressure. When the front coverincluding the friction surface is deformed, the entire surface of thefriction member becomes incapable of evenly making contact with thefriction surface. Accordingly, the friction member is locally abraded,and this becomes a cause of abnormal abrasion.

In view of this, in Japan Laid-open Patent Application Publication No.2012-211707, a slide member having an annular shape is fixed to thesurface of the front cover in opposition to the clutch part, wherebydegradation in stiffness of the front cover is inhibited, andconsequently, deformation of the front cover is inhibited.

BRIEF SUMMARY

In the device of Japan Laid-open Patent Application Publication No.2012-211707, the slide member is fixed to the front cover so as toinhibit the front cover, especially, the friction surface thereof frombeing deformed.

However, a member with high stiffness is required for reliablyinhibiting deformation of the friction surface, and herein, the devicenot only becomes heavy but also is elongated in axial dimension. On theother hand, increase in internal pressure of the torque converter bringsabout deformation of the front cover such as bulging of mainly the innerperipheral part of the front cover. It is difficult to inhibit suchdeformation only by fixing the slide member to the friction surface.

It is an object of the present disclosure to enable the entire surfaceof a friction member to evenly make contact with a friction surface of afront cover with a simple configuration even when the front cover isdeformed by increase in internal pressure of a torque converter.

(1) A lock-up device for a torque converter according to an aspect ofthe present disclosure is a device for transmitting a torque from afront cover to a transmission-side member through a turbine of thetorque converter. The lock-up device includes a friction surfaceprovided on a lateral surface of the front cover, a clutch disc, whichhas an annular shape and is capable of being pressed in contact with thefriction surface, a piston, and a pressure plate having an annularshape. The piston is disposed between the front cover and the turbine,and is movable in an axial direction. The pressure plate is disposedbetween the piston and the clutch disc so as to be movable in the axialdirection, and presses the clutch disc toward the front cover by apressing force applied thereto from the piston. Additionally, thepressure plate has a lower bending stiffness than the piston, and isdeformable in accordance with deformation of the front cover whenpressed toward the front cover by the piston.

Here, when the piston is moved toward the front cover, the clutch discis pressed in contact with the friction surface of the front coverthrough the pressure plate, and a lock-up on state (a power transmissionactivated state) is made.

Here, when the interval pressure of the torque converter has increased,the front cover has been deformed, for instance, such that the innerperipheral side part of the friction surface is closer to the enginethan the outer peripheral side part thereof. In such a condition, whenpressed toward the friction surface by the piston, the pressure plateand the clutch disc are deformed in accordance with deformation of thefront cover because the stiffness of the pressure plate is set to below. With this deformation, the entire surface of the clutch disc issupposed to make contact with the friction surface. Therefore, with thesimple configuration, part of the clutch disc can be inhibited frombeing abnormally abraded.

(2) Preferably, the clutch disc includes a core plate having an annularshape and friction members fixed to both lateral surfaces of the coreplate. The core plate has a lower bending stiffness than the pressureplate, and is deformable in accordance with the deformation of the frontcover when pressed toward the front cover by the piston and the pressureplate.

Similarly to the above, under the assumption that the front cover hasbeen deformed, when the clutch disc is herein pressed by the piston andthe pressure plate, the core plate is deformed in accordance with thedeformation of the front cover. With this deformation, the entiresurface of the friction member makes contact with the friction surface.Hence, with the simple configuration, the friction member can beinhibited from being abnormally abraded.

(3) Preferably, the piston includes a body having a disc shape and apressure applying part. The pressure applying part is included in anouter peripheral part of the body so as to protrude in the axialdirection, and presses the pressure plate. Additionally, the pressureapplying part presses the pressure plate by making contact with a regionof the friction member, which ranges between a position shifted to aninner peripheral side from a middle of a radial width of the frictionmember by 20% of the radial width and a position shifted to an outerperipheral side from the middle of the radial width of the frictionmember by 10% of the radial width.

When the internal pressure of the torque converter has increased, thefront cover has been generally deformed such that the inner peripheralside part of the friction member is closer to the engine than the outerperipheral side part thereof. In such a condition, it is more preferablefor the piston to press the inner peripheral side part of the frictionmember than to press the outer peripheral side part of the frictionmember.

Specifically, when the friction member is pressed at an outer peripheralregion thereof corresponding to 40% of the radial width thereof, theinner peripheral side part of the clutch disc including the frictionmember is likely to be deformed in a direction separating from the frontcover, and the entire surface of the friction member is prevented frommaking contact with the friction surface. On the other hand, when thefriction member is pressed at an inner peripheral region thereofcorresponding to 30% of the radial width thereof, the outer peripheralside part of the clutch disc including the friction member is likely tobe deformed in the direction separating from the front cover, and theentire surface of the friction member is prevented from making contactwith the friction surface.

In view of this, for the purpose of causing the entire surface of thefriction member to make contact with the friction surface, it ispreferable for the friction member to be pressed at the region thereofranging from the position shifted to the inner peripheral side from themiddle of the radial width of the friction member by 20% of the radialwidth and the position shifted to the outer peripheral side from themiddle of the radial width by 10% of the radial width.

(4) Preferably, the lock-up device further includes a damper mechanismthat transmits the torque from the clutch disc therethrough to theturbine, and also, absorbs and attenuates a torsional vibration.

(5) Preferably, the pressure plate receives the torque inputted theretofrom the front cover, and the clutch disc transmits the torque from thepressure plate and the front cover therethrough to the damper mechanism.

Here, the torque from the front cover is transmitted to the pressureplate. The torque is further transmitted from the pressure plate to theclutch disc by frictional transmission, and is transmitted to the dampermechanism.

(6) Preferably, the lock-up device further includes a support bosshaving an annular shape and an oil chamber plate having a disc shape.The support boss is fixed to an inner peripheral part of the front coverso as to protrude toward the turbine, and also, supports the piston onan outer peripheral surface thereof such that the piston is slidable inthe axial direction. The oil chamber plate is fixed to the outerperipheral surface of the support boss such that the piston isinterposed between the front cover and the oil chamber plate, and formsa lock-up oil chamber together with the piston therebetween.

Here, the piston is actuated by supplying hydraulic oil to the lock-upoil chamber, whereby the lock-up on state can be quickly made.

(7) Preferably, the oil chamber plate includes a torque transmissionpart transmitting the torque from the front cover therethrough to thepressure plate.

Here, the torque inputted to the front cover is transmitted from thesupport boss to the pressure plate through the torque transmission partof the oil chamber plate, and is further transmitted from the pressureplate to the damper mechanism through the clutch disc.

(8) Preferably, the piston includes a plurality of openings thatpenetrate therethrough in the axial direction and are aligned atpredetermined intervals in a circumferential direction. Additionally,the torque transmission part is integrated with the oil chamber plateand is included in an outer peripheral part of the oil chamber plate.The torque transmission part is engaged with the pressure plate whilepenetrating the plurality of openings of the piston.

(9) Preferably, the front cover and the piston form a cancellation oilchamber therebetween so as to cancel a hydraulic pressure to begenerated in the lock-up oil chamber when a lock-up state is released.Additionally, the support boss includes an oil passage communicated withthe lock-up oil chamber and an oil passage communicated with thecancellation oil chamber.

Here, the lock-up on state is released by draining the hydraulic oil inthe lock-up oil chamber. Then, the cancellation oil chamber cancels thehydraulic pressure to be generated by a centrifugal force acting on thehydraulic oil remaining in the lock-up oil chamber when a lock-up offstate is made. Additionally, the cancellation oil chamber is configuredby utilizing the front cover, and hence, the configuration thereof ismade simple.

According to the above, even when a front cover is deformed by increasein internal pressure of a torque converter, the entire surface of afriction member is enabled to evenly make contact with a frictionsurface of the front cover with a simple structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional configuration diagram of a torque converterincluding a lock-up device according to an exemplary embodiment of thepresent disclosure.

FIG. 2 is a diagram showing part extracted from FIG. 1.

FIG. 3 is a diagram of a clutch disc shown in detail.

FIG. 4 is a partial front view of an engaging part between a pressureplate and a cover plate.

FIG. 5 is a partial front view of an engaging part between a piston andthe cover plate.

FIG. 6 is an enlarged view of part extracted from FIG. 1.

FIG. 7 is an external perspective view of an engaging structure betweenthe piston and the cover plate.

FIG. 8 is a cross-sectional plan view of a return mechanism.

FIG. 9 is a cross-sectional configuration diagram for explaining adamper mechanism.

DETAILED DESCRIPTION OF EMBODIMENTS

[Entire Configuration of Torque Converter]

FIG. 1 is a vertical cross-sectional view of a torque converter 1employing an exemplary embodiment of the present disclosure. The torqueconverter 1 is a device that transmits a torque from a crankshaft of anengine to an input shaft of a transmission. In FIG. 1, the engine (notshown in the drawing) is disposed on the left side, whereas thetransmission (not shown in the drawing) is disposed on the right side.Line 0-0 depicted in FIG. 1 is a rotational axis of the torque converter1.

The torque converter 1 mainly includes a front cover 2, a torqueconverter body 6 composed of three types of bladed wheels (an impeller3, a turbine 4 and a stator 5) and a lock-up device 7.

[Front Cover 2]

The front cover 2 is a disc-shaped member and a center boss 8 is fixedto the inner peripheral end of the front cover 2 by welding. The centerboss 8 is a cylindrical member extending in the axial direction, and isinserted into a center hole of the crankshaft (not shown in thedrawings).

It should be noted that the front cover 2 is configured to be coupled tothe crankshaft of the engine through a flexible plate, although theconfiguration is not shown in the drawings. In other words, a pluralityof bolts 9 are fixed to the engine-side surface of the outer peripheralpart of the front cover 2, while being aligned at equal intervals in thecircumferential direction. The outer peripheral part of the flexibleplate is fixed to the front cover 2 by nuts screwed onto the bolts 9.

The front cover 2 includes an outer peripheral side tubular part 2 a inthe outer peripheral part thereof. The outer peripheral side tubularpart 2 a extends axially toward the transmission. The impeller 3 isfixed to the distal end of the outer peripheral side tubular part 2 a bywelding. As a result, a fluid chamber, the interior of which is filledwith hydraulic oil, is formed by the front cover 2 and the impeller 3.

Additionally, the front cover 2 includes a flat part 2 b having anannular shape on the turbine-side lateral surface of the radiallyintermediate part thereof. The flat part 2 b is shaped to protrudetoward the turbine than parts located on the inner and outer peripheralsides thereof. The surface of the flat part 2 b functions as a frictionsurface (the flat part 2 b will be hereinafter referred to as “frictionsurface 2 b”).

[Impeller 3]

The impeller 3 is mainly composed of an impeller shell 10 and aplurality of impeller blades 11 fixed to the inside of the impellershell 10. Additionally, the outer peripheral side distal end of theimpeller shell 10 is welded to the front cover 2 as described above. Itshould be noted that the impeller shell 10 includes a tubular part inthe inner peripheral end thereof. The tubular part extends toward thetransmission.

[Turbine 4]

The turbine 4 is disposed in axial opposition to the impeller 3 withinthe fluid chamber. The turbine 4 is mainly composed of a turbine shell14, a plurality of turbine blades 15 fixed to the inside of the turbineshell 14, and a turbine hub 16 fixed to the inner peripheral end of theturbine shell 14. The turbine shell 14 and the turbine hub 16 are fixedby a plurality of rivets 17.

The turbine hub 16 includes a flange part 16 a, a tubular part 16 b anda damper support part 16 c. The flange part 16 a is a disc-shaped partto which the inner peripheral end of the turbine shell 14 is fixed. Thetubular part 16 b is shaped to extend from the inner peripheral part ofthe flange part 16 a toward the transmission. The tubular part 16 bincludes a spline hole 16 d in the inner peripheral part thereof, andthe spline hole 16 d is capable of being meshed with a spline shaftprovided on the tip of the input shaft of the transmission (not shown inthe drawings). The damper support part 16 c is formed by extending theouter peripheral part of the flange part 16 a. The damper support part16 c will be described below in detail.

A collar 18 is fixed to the inner peripheral end of the turbine hub 16on the opposite side (the engine side) of the tubular part 16 b. On theinner peripheral end of the turbine hub 16, the collar 18 extends towardthe engine from approximately the same radial position as the tubularpart 16 b.

[Stator 5]

The stator 5 is a mechanism disposed between the inner peripheral partof the impeller 3 and that of the turbine 4 so as to regulate the flowof hydraulic oil returning from the turbine 4 to the impeller 3. Thestator 5 is made by integral casting of resin, aluminum alloy or soforth. The stator 5 mainly includes a stator shell 20 having a discshape and a plurality of stator blades 21 integrated with the statorshell 20 on the outer peripheral side of the stator shell 20. The statorshell 20 is coupled to a stationary shaft (not shown in the drawings)through a one-way clutch 22.

A thrust bearing 23 is disposed between the stator shell 20 and theimpeller shell 10, whereas a thrust bearing 24 is disposed between thestator shell 20 and the flange part 16 a of the turbine hub 16.

[Lock-Up Device 7]

The lock-up device 7 is a device disposed between the front cover 2 andthe turbine 4 so as to directly transmit power from the front cover 2 tothe turbine 4. As shown close-up in FIG. 2, the lock-up device 7includes a clutch disc 28, a pressure plate 29, a piston 30, a pistonactuation mechanism 31 and a damper mechanism 34.

<Clutch Disc 28>

The clutch disc 28 has an annular shape and is capable of being pressedin contact with the friction surface 2 b of the front cover 2. Theclutch disc 28 includes a core plate 36 having an annular shape andfriction members 37 that have an annular shape and are fixed to bothlateral surfaces of the core plate 36. The core plate 36 has an outerperipheral part larger than the outer diameter of each friction member37, and is bent at a predetermined angle toward the turbine at a partthereof protruding to the outer peripheral side beyond the frictionmembers 37. Additionally, the bent part includes a plurality of engagingprotrusions 36 a.

Additionally, as shown close-up in FIG. 3, the clutch disc 28 is shapedto tilt in a free state that a lock-up off state (a power transmissiondeactivated state) is made. Specifically, the clutch disc 28 tilts suchthat the inner peripheral side part thereof is located closer to thefront cover 2 than the outer peripheral side part thereof. Therefore,when the lock-up off state is made, the inner peripheral end of theclutch disc 28 annularly makes line contact with the friction surface 2b of the front cover 2, whereas the outer peripheral end of the clutchdisc 28 annularly makes line contact with the pressure plate 29. Withthe configuration described above, a drag torque is lessened when thelock-up off state is made.

<Pressure Plate 29>

The pressure plate 29 is disposed between the clutch disc 28 and thepiston 30 so as to be movable in the axial direction. The pressure plate29 is pressed by the piston 30, and thereby presses the clutch disc 28toward the front cover 2. Additionally, the pressure plate 29 has anannular shape, and the outer diameter thereof is larger than that ofeach friction member 37 of the clutch disc 28, while the inner diameterthereof is smaller than that of each friction member 37. As shownclose-up in FIG. 4, the pressure plate 29 includes a plurality ofgrooves 29 a on the inner peripheral end thereof. The grooves 29 a arealigned at predetermined intervals in the circumferential direction.Each groove 29 a has a predetermined depth in the radial direction andis opened to the inner peripheral side. It should be noted that FIG. 4is a view of the pressure plate 29 as seen from the front cover 2 side.

<Piston 30>

As shown in FIGS. 1 and 2, the piston 30 is disposed between the frontcover 2 and the turbine 4 and is movable in the axial direction. Thepiston 30 includes a pressure receiving part 30 a having a disc shape, afirst protruding part 30 b, a second protruding part 30 c and an outerperipheral disc part 30 d. It should be noted that the body thereof iscomposed of the pressure receiving part 30 a and the outer peripheraldisc part 30 d.

The pressure receiving part 30 a is a part that receives the pressure ofhydraulic oil, and the first protruding part 30 b is included in theouter peripheral part of the pressure receiving part 30 a so as toprotrude toward the turbine 4. The outer peripheral end of the pressurereceiving part 30 a slantingly extends toward the front cover 2, and thesecond protruding part 30 c is included in the distal end of thisslantingly extending part so as to further protrude therefrom toward thefront cover 2.

The outer peripheral disc part 30 d is integrated with the pressurereceiving part 30 a, and is shifted (off-set) to the front cover sidewith respect to the pressure receiving part 30 a. As shown in FIG. 5,the outer peripheral disc part 30 d includes a plurality of openings 30e in the inner peripheral part thereof. The openings 30 e are aligned atpredetermined intervals in the circumferential direction. The pluralopenings 30 e axially penetrate therethrough. It should be noted thatFIG. 5 is a view of the piston 30 as seen from the front cover 2 side.

Additionally, the outer peripheral disc part 30 d includes a pressureapplying part 30 f having an annular shape in the outer peripheral endthereof. The pressure applying part 30 f is included in the outerperipheral end of the outer peripheral disc part 30 d so as to protrudetoward the front cover 2. The pressure applying part 30 f is shaped tomake contact with the approximately middle of the radial width of thepressure plate 29. Preferably, the pressure applying part 30 f presses,through the pressure plate 29, a region of one friction member 37ranging between a position shifted to the inner peripheral side from themiddle of the radial width of the friction member 37 by 20% of theradial width and a position shifted to the outer peripheral side fromthe middle of the radial width of the friction member 37 by 10% of theradial width (i.e., a region of 30 to 60, where the inner peripheral endof the radial width of the friction member 37 is set as “0” and theouter peripheral end thereof is set as “100”).

<Stiffness of Core Plate 36, Pressure Plate 29 and Piston 30>

Regarding the bending stiffness of the core plate 36, that of thepressure plate 29, and that of the piston 30, the piston 30 is set to bethe highest; the pressure plate 29 is set to be lower than the piston30; and the core plate 36 is set to be the lowest.

The specifications of the core plate 36, the pressure plate 29 and thepiston 30 are set as described above. Hence, when pressed by the piston30 while the front cover 2 (especially, the part thereof including thefriction surface 2 b) has been deformed, the pressure plate 29 and theclutch disc 28 are supposed to be deformed in accordance with thedeformed front cover 2.

<Piston Actuation Mechanism 31>

The piston 30 is axially actuated by the piston actuation mechanism 31.As shown in FIG. 2, the piston actuation mechanism 31 includes a supportboss 40, a cover plate 41 (an oil chamber plate) and a return mechanism42.

Support Boss 40

As shown in FIGS. 2 and 6, the support boss 40 is fixed to the innerperipheral part of the front cover 2. Specifically, the support boss 40is part of the center boss 8, and is made in the shape of a tube axiallyextending from the turbine 4-side end of the center boss 8. The supportboss 40 includes a first fixation part 40 a, a piston support part 40 b,a second fixation part 40 c, a first intermediate part 40 d and a secondintermediate part 40 e. It should be noted that FIG. 6 is a partialenlarged view of FIG. 1.

The inner peripheral end surface of the front cover 2 is fixed to theouter peripheral surface of the first fixation part 40 a by welding. Inother words, the inner peripheral end surface of the front cover 2 isinserted and fixed onto the outer peripheral surface of the firstfixation part 40 a, whereby the front cover 2 is radially positionedwith respect to the center boss 8.

The piston support part 40 b has an outer diameter larger than that ofthe first fixation part 40 a. The inner peripheral end surface of thepiston 30 is supported by the outer peripheral surface of the pistonsupport part 40 b so as to be slidable thereon. Additionally, a sealmember 45 is attached to the outer peripheral surface of the pistonsupport part 40 b. The seal member 45 seals between the outer peripheralsurface of the piston support part 40 b and the inner peripheral endsurface of the piston 30. It should be noted that the front cover 2-sidelateral surface of the piston support part 40 b tilts to graduallyseparate away from the front cover 2 to the inner peripheral side.

The second fixation part 40 c has an outer diameter smaller than that ofthe piston support part 40 b. In other words, the piston support part 40b and the second fixation part 40 c compose a step. The inner peripheralend surface of the cover plate 41 is fixed to the outer peripheralsurface of the second fixation part 40 c by welding. Even when the coverplate 41 is welded to the second fixation part 40 c, welding-relatedstrain of the piston support part 40 b can be inhibited by setting theouter diameter of the second fixation part 40 c to be smaller than thatof the piston support part 40 b to which the seal member 45 is attached.Therefore, sealing performance between the piston support part 40 b andthe piston 30 is enhanced.

The first intermediate part 40 d is provided between the first fixationpart 40 a and the piston support part 40 b. The outer peripheral surfaceof the first intermediate part 40 d tilts such that the diameter thereofgradually increases from the front cover 2 side to the turbine 4 side.The minimum diameter of the outer peripheral surface of the firstintermediate part 40 d is larger than the diameter of the first fixationpart 40 a, while the maximum diameter thereof is smaller than thediameter of the piston support part 40 b.

The second intermediate part 40 e is provided between the piston supportpart 40 b and the second fixation part 40 c. The outer peripheralsurface of the second intermediate part 40 e tilts such that thediameter thereof gradually reduces from the front cover 2 side to theturbine 4 side. The maximum diameter of the outer peripheral surface ofthe second intermediate part 40 e is smaller than the diameter of thepiston support part 40 b, while the minimum diameter thereof is largerthan the diameter of the second fixation part 40 c.

It should be noted that a thrust washer 46 is disposed between theturbine 4-side end surface of the support boss 40 and the turbine hub16. The thrust washer 46 includes at least one radial groove on asurface thereof.

Cover Plate 41

The cover plate 41 is disposed such that the pressure receiving part 30a of the piston 30 is interposed between the cover plate 41 and thefront cover 2. As shown in FIG. 2, the cover plate 41 includes a body 41a, a seal part 41 b and a torque transmission part 41 c.

The body 41 a has a disc shape, and as described above, the innerperipheral end surface thereof is fixed to the outer peripheral surfaceof the second fixation part 40 c of the support boss 40 by welding.

The seal part 41 b is included in the outer peripheral part of the body41 a, and includes a recess 41 d dented therefrom toward the turbine 4.The first protruding part 30 b of the piston 30 is inserted into therecess 41 d. A seal member 47 is attached to the outer peripheral partof the first protruding part 30 b, and the outer peripheral part thereofmakes contact with the inner peripheral surface of the recess 41 d.Therefore, a lock-up oil chamber C1 is formed between the piston 30 andthe cover plate 41 by the seal member 47.

The torque transmission part 41 c is provided on the further outerperipheral side of the seal part 41 b. The torque transmission part 41 cis composed of a plurality of engaging protrusions (hereinafter referredto as “engaging protrusions 41 c”) extending from the outer peripheralpart of the seal part 41 b to the front cover side. As shown in FIGS. 4and 5, the engaging protrusions 41 c penetrate the openings 30 eprovided in the piston 30, and are engaged with the grooves 29 aprovided on the inner peripheral end of the pressure plate 29. FIG. 7shows a perspective view of the cover plate 41 and the piston 30 as seenfrom the turbine 4 side.

With the configuration described above, a torque transmitted to thecover plate 41 can be transmitted to the pressure plate 29.Additionally, rotation of the piston 30 relative to the cover plate 41can be restricted by appropriately setting the circumferential dimensionof each of the engaging protrusions 41 c as the torque transmission partand the circumferential dimension of each of the openings 30 e of thepiston 30.

Return Mechanism 42

As shown in FIGS. 2 and 8, the return mechanism 42 is disposed betweenthe front cover 2 and the piston 30. FIG. 8 is a cross-sectional planview showing part of both the front cover 2 and the piston 30, in whichthe return mechanism 42 is disposed, as seen from the outer peripheralside. Specifically, the return mechanism 42 is disposed between a recess2g provided on the piston 30-side lateral surface of the front cover 2and a recess 30 g provided on the front cover 2-side lateral surface ofthe piston 30. The return mechanism 42 is a mechanism that urges thepiston 30 in a direction separating from the friction surface of thefront cover 2. The return mechanism 42 urges the piston 30 in thedirection separating from the front cover 2 and adjusts the gap betweenthe friction surface 2 b of the front cover 2 and the pressure applyingpart 30 f of the piston 30. As shown in FIG. 8, the return mechanism 42is composed of a return spring 50 made of bimetal and a cam mechanism51.

The return spring 50 is disposed to extend in the right-and-leftdirection between a support member 52 fixed to the front cover 2 and oneend of the cam mechanism 51. As shown in FIG. 8(a), when the temperatureof hydraulic oil is low, the return spring 50 deforms such that thespring length thereof becomes short. On the other hand, as shown in FIG.8(b), when the temperature of hydraulic oil is high, the return spring50 deforms such that the spring length thereof becomes long.

The cam mechanism 51 includes a first cam member 55 fixed to the recess2g of the front cover 2 and a second cam member 56 fixed to the recess30 g of the piston 30.

The first cam member 55 is a member made in the shape of a blockextending in the right-and-left direction, and includes a first slope 55a, a groove 55 b and a second slope 55 c. The first slope 55 a isprovided on the outer peripheral surface of one end of the first cammember 55 and slants such that the thickness thereof gradually reducesfrom one end thereof to the other end thereof. The groove 55 b isprovided on the other end side of the first slope 55 a, has apredetermined width, and penetrates in the radial direction. The secondslope 55 c is provided on the inner peripheral surface of a protrudingpart provided to cover part of the groove 55 b on the other end side.The second slope 55 c slants in the same direction as the first slope 55a. One end of the return spring 50 is fixed to the other end surface ofthe first cam member 55.

The second cam member 56 is a member made in the shape of a blockextending in the right-and-left direction, and includes a first slope 56a, an engaging part 56 b and a second slope 56 c. The engaging part 56 bis a part of the second cam member 56 and protrudes toward the first cammember 55. The engaging part 56 b is capable of being inserted into thegroove 55 b of the first cam member 55. Additionally, the first slope 56a is provided on the first cam member 55-side part of the engaging part56 b, and slants in the same direction at the same angle as the firstslope 55 a of the first cam member 55. Moreover, the first slopes 55 aand 56 a of both cam members 55 and 56 are slidable in contact with eachother. On the other hand, the second slope 56 c is provided on theengaging part 56 b so as to be located on the opposite side of the firstslope 56 a, and slants in the same direction at the same angle as thesecond slope 55 c of the first cam member 55. Additionally, the secondslopes 55 c and 56 c of both cam members 55 and 56 are slidable incontact with each other.

Working of Return Mechanism 42

In the return mechanism 42 described above, when the atmospheretemperature is low, the return spring 50 contracts as shown in FIG.8(a). Therefore, in FIG. 8(a), the first cam member 55 is movedrightward with respect to the second cam member 56. Accordingly, thepiston 30 is moved to separate from the front cover 2 by sliding betweenthe first slopes 55 a and 56 a of the first and second cam members 55and 56. Therefore, the gap between the piston 30 and the front cover 2,in other words, the gap of the part that the clutch disc 28 is provided(the release allowance of the clutch disc 28) is increased.Consequently, the drag torque can be inhibited low in the part inclusiveof the clutch disc 28.

On the other hand, when the atmosphere temperature becomes high, and forinstance, becomes a room temperature, the return spring 50 expands asshown in FIG. 8(b). Therefore, in FIG. 8(b), the first cam member 55 ismoved leftward with respect to the second cam member 56. Accordingly,the piston 30 is moved to approach to the front cover 2 by slidingbetween the second slopes 55 c and 56 c of the first and second cammembers 55 and 56. Therefore, the gap between the piston 30 and thefront cover 2, in other words, the gap of the part that the clutch disc28 is provided (the release allowance of the clutch disc 28) is reduced.Consequently, a lock-up on state can be quickly made.

<Hydraulic Circuit>

With the configuration of the piston actuation mechanism 31, as shown inFIG. 2, the lock-up oil chamber C1 is formed between the pressurereceiving part 30 a of the piston 30 and the body 41 a of the coverplate 41. Additionally, the front cover 2 includes a step part 2 c,having an axially extending tubular shape, between the radiallyintermediate part thereof and the inner peripheral part thereof. A sealmember 57 is attached to the outer peripheral surface of the step part 2c. The seal member 57 makes contact with the inner peripheral surface ofthe second protruding part 30 c of the piston 30. Therefore, acancellation oil chamber C2 is formed between the pressure receivingpart 30 a of the piston 30 and the front cover 2 so as to cancel thehydraulic pressure to be generated in the lock-up oil chamber C1 whenthe lock-up off state is made.

It should be noted that the seal member 57, attached to the step part 2c of the front cover 2, exerts sealing performance inferior to that of anormal seal member (e.g., the seal member 47 attached to the firstprotruding part 30 b). Specifically, even when the seal member 57 isattached to the step part 2 c, the gap of the part that the seal member57 is abutted to the object thereof is set to be wider than a normallyset gap. Therefore, a larger amount of hydraulic oil leaks in the partthat the seal member 57 is attached than in the other sealed parts.

As shown in FIGS. 2 and 6, the support boss 40 includes a first oilpassage P1 and a second oil passage P2, both of which radially penetratetherethrough. The first oil passage P1 is opened in the slope of thesecond intermediate part 40 e of the support boss 40, and the lock-upoil chamber C1 and the space of the inner peripheral part of the supportboss 40 are communicated therethrough. The second oil passage P2 isopened in the slope of the first intermediate part 40 d, and thecancellation oil chamber C2 and the space of the inner peripheral partof the support boss 40 are communicated therethrough. The collar 18includes a groove 18 a having an annular shape, and the groove 18 aincludes a plurality of third oil passages P3 radially penetratingtherethrough. Additionally, the second oil passage P2 is communicatedwith the third oil passages P3.

<Damper Mechanism 34>

The damper mechanism 34 is a mechanism disposed between the clutch disc28 and the turbine 4 so as to transmit a torque from the clutch disc 28to the turbine 4. As shown in FIG. 9, the damper mechanism 34 includesan engaging member 60, a drive plate 61, a driven plate 62 and aplurality of torsion springs 63.

The engaging member 60 includes a fixed part 60 a, a plurality of firstengaging parts 60 b and a plurality of second engaging parts 60 c. Thefixed part 60 a has an annular shape and is fixed to the drive plate 61by rivets 65. The plural first engaging parts 60 b are formed by bendingthe outer peripheral end of the fixed part 60 a toward the front cover2, and are meshed with the engaging protrusions 36 a provided on theouter periphery of the core plate 36 of the clutch disc 28. The clutchdisc 28 is axially movable with respect to the first engaging parts 60b, but is prevented from rotating relatively thereto. The plural secondengaging parts 60 c are formed by bending the outer peripheral end ofthe fixed part 60 a toward the turbine 4.

The drive plate 61 has an annular shape, and is disposed between thepiston 30 and the turbine 4. The drive plate 61 transmits a torque,transmitted to the engaging member 60, to the torsion springs 63. Thedrive plate 61 includes a disc part 61 a, a plurality of support parts61 b and a plurality of engaging parts 61 c.

The inner peripheral end surface of the disc part 61 a is bent towardthe turbine 4, and is provided as a positioning part 61 d. Thepositioning part 61 d is supported by the damper support part 16 cprovided on the outer peripheral end of the turbine hub 16, and ispositioned in the radial direction and the axial direction. The discpart 61 a includes holes 61 e axially penetrating the outer peripheralpart thereof. The second engaging parts 60 c of the engaging member 60extend toward the turbine 4 while penetrating the holes 61 e.

The support parts 61 b are included in the outer peripheral part of thedisc part 61 a and have a C-shaped cross-section. The plural torsionsprings 63 are accommodated in the support parts 61 b, and arerestricted from moving in the radial direction and from moving towardthe front cover 2 by the support parts 61 b.

The engaging parts 61 c are included in the outer peripheral part of thedisc part 61 a, and each is provided between adjacent two of the supportparts 61 b. The engaging parts 61 c are partially engaged with both endsurfaces of the torsion springs 63 accommodated in the support parts 61b.

The driven plate 62 has a roughly disc shape, and is disposed betweenthe drive plate 61 and the turbine 4. The driven plate 62 is a memberthat transmits a torque, transmitted to the torsion springs 63, to theturbine hub 16. The driven plate 62 is fixed at the inner peripheral endthereof to the turbine shell 14 and the turbine hub 16 by the rivets 17.Additionally, the driven plate 62 extends to the outer peripheral sidealong the lateral surface of the turbine shell 14. Engaging parts 62,included in the outer peripheral part of the drive plate 62, are engagedwith both end surfaces of the torsion springs 63.

[Actions]

For lock-up releasing (the lock-up off state) in the lock-up device 7,the lock-up oil chamber C1 is connected to a drain. Therefore, thehydraulic oil inside the lock-up oil chamber C1 is returned to a tankside through the first oil passage P1. In this condition, a pressingforce applied to the pressure plate 29 from the pressure applying part30 f of the piston 30 is released. Therefore, the lock-up off state (thepower transmission deactivated state) is made, and the torque from thefront cover 2 is transmitted from the impeller 3 to the turbine 4through the hydraulic oil, and is transmitted to the input shaft of thetransmission through the turbine hub 16.

It should be noted that when the lock-up off state is made, chances arethat a centrifugal force acts on the hydraulic oil remaining in thelock-up oil chamber C1 whereby the piston 30 is pressed toward the frontcover 2. When the piston 30 is moved toward the front cover 2, the dragtorque due to the clutch disc 28 is increased.

To cope with this, in the present device, as described above, the amountof leakage through the seal member 57 is set to be larger than thatthrough a normal seal member. With this setting, the hydraulic oilleaking through the seal member 57 intrudes into the cancellation oilchamber C2, whereby the piston 30 is inhibited from moving toward thefront cover 2. In other words, the pressing force acting on the piston30 due to the centrifugal force acting on the hydraulic oil in thelock-up oil chamber C1 is configured to be canceled by the hydraulic oilleaking through the seal member 57 into the cancellation oil chamber C2.

On the other hand, when the lock-up on state (a power transmissionactivated state) is made in the lock-up device 7, the cancellation oilchamber C2 is connected to the drain, and simultaneously, the hydraulicoil is supplied to the lock-up oil chamber C1. In other words, thehydraulic oil is supplied to the end surface of the collar 18, andsimultaneously, the hydraulic oil is supplied to the lock-up oil chamberC1 through the first oil passage P1. The piston 30 is thereby movedtoward the front cover 2, and moves the pressure plate 29 toward thefront cover 2. Accordingly, the clutch disc 28 is interposed and heldbetween the front cover 2 and the pressure plate 29, and the lock-up onstate is made.

When the lock-up on state is made, the torque from the front cover 2 istransmitted to the damper mechanism 34 through a path of “the supportboss 40→the cover plate 41→the pressure plate 29→the clutch disc 28”,and is also transmitted from the front cover 2 to the damper mechanism34 through the clutch disc 28.

In the aforementioned torque transmission path, a torque is transmittedbetween the cover plate 41 and the pressure plate 29 by meshing betweenthe engaging protrusions 41 c and the grooves 29 a. A gap exists betweeneach engaging protrusion 41 c and each groove 29 a, whereby clickingsound is produced. The clicking sound is supposed to be transmitted tothe front cover 2 and then leak to the outside. However, in the deviceof the present exemplary embodiment, a long transmission path is setbetween the front cover 2 and the parts that the clicking sound isproduced (engaging parts between the engaging protrusions 41 c and thegrooves 29 a). Hence, the clicking sound is attenuated until transmittedto the front cover 2. Therefore, the clicking sound becomes unlikely toleak to the outside.

In the damper mechanism 34, the torque inputted to the engaging member60 is transmitted to the turbine 4 through the torsion springs 63 andthe driven plate 62, and is further transmitted to the input shaft ofthe transmission through the turbine hub 16.

During actuation of the lock-up device 7 described above, the frontcover 2 has chances of being deformed by the pressure of hydraulic oiland/or the centrifugal force such that the inner peripheral part thereoffurther expands than the outer peripheral part thereof. When the clutchdisc 28 is pressed in contact with the front cover 2 while the frontcover 2 (especially, the friction surface 2 b) is deformed, it isconcerned that the clutch disc 28 locally makes contact with the frontcover 2 without entirely making contact therewith and is therebyabnormally abraded.

However, in the present device, the relation “the piston 30>the pressureplate 29>the core plate 36” is set regarding the bending stiffness ofthe core plate 36, that of the pressure plate 29, and that of the piston30. Hence, even when the front cover 2 is deformed, the pressure plate29 and the clutch disc 28 are configured to be deformed in accordancewith deformation of the front cover 2 by pressing the pressure plate 29and the clutch disc 28 with the piston 30. With this configuration, theclutch disc 28 can be inhibited from being abnormally abraded.

Other Exemplary Embodiments

The present disclosure is not limited to the exemplary embodimentdescribed above, and a variety of changes or modifications can be madewithout departing from the scope of the present disclosure.

In the aforementioned exemplary embodiment, the clutch part is composedof the clutch disc 28. However, for instance, a friction member may befixed to the lateral surface of the pressure plate, and the frictionmember may be configured to be pressed in contact with the frictionsurface 2 b of the front cover 2. In this case, a clutch disc can beomitted.

On the other hand, the return mechanism for separating the piston fromthe front cover may be disposed between the piston and the cover plate.

INDUSTRIAL APPLICABILITY

In the lock-up device of the present disclosure, even when a front coveris deformed by increase in internal pressure of a torque converter, theentire surface of a friction member is enabled to evenly make contactwith a friction surface of the front cover with a simple structure.

REFERENCE SIGNS LIST

-   2 Front cover-   2 b Friction surface-   4 Turbine-   28 Clutch disc-   29 Pressure plate-   29 a Groove-   30 Piston-   30 a Pressure receiving part-   30 e Opening-   30 f Pressure applying part-   34 Damper mechanism-   36 Core plate-   37 Friction member-   40 Support boss-   41 Cover plate (oil chamber plate)-   41 c Engaging protrusion (torque transmission part)-   C1 Lock-up oil chamber-   C2 Cancellation oil chamber-   P1 First oil passage-   P2 Second oil passage-   P3 Third oil passage

1. A lock-up device for a torque converter, the lock-up device fortransmitting a torque from a front cover to a transmission-side memberthrough a turbine of the torque converter, the lock-up devicecomprising: a friction surface provided on a lateral surface of thefront cover; a clutch disc having an annular shape, the clutch disccapable of being pressed in contact with the friction surface; a pistondisposed between the front cover and the turbine, the piston beingmovable in an axial direction; and a pressure plate having an annularshape, the pressure plate disposed between the piston and the clutchdisc so as to be movable in the axial direction, the pressure plate forpressing the clutch disc toward the front cover by a pressing force tobe applied thereto from the piston, wherein the pressure plate has alower bending stiffness than the piston, the pressure plate deformablein accordance with deformation of the front cover when pressed towardthe front cover by the piston.
 2. The lock-up device for a torqueconverter according to claim 1, wherein the clutch disc includes a coreplate having an annular shape and friction members fixed to both lateralsurfaces of the core plate, and the core plate has a lower bendingstiffness than the pressure plate, the core plate deformable inaccordance with the deformation of the front cover when pressed towardthe front cover by the piston and the pressure plate.
 3. The lock-updevice for a torque converter according to claim 2, wherein the pistonincludes a body having a disc shape, and a pressure applying partincluded in an outer peripheral part of the body so as to protrude inthe axial direction, the pressure applying part for pressing thepressure plate, and the pressure applying part presses the pressureplate by making contact with a region of the friction member, the regionranging between a position shifted to an inner peripheral side from amiddle of a radial width of the friction member by 20% of the radialwidth and a position shifted to an outer peripheral side from the middleof the radial width of the friction member by 10% of the radial width.4. The lock-up device for a torque converter according to claim 1,further comprising: a damper mechanism for transmitting the torque fromthe clutch disc therethrough to the turbine, the damper mechanism forabsorbing and for attenuating a torsional vibration.
 5. The lock-updevice for a torque converter according to claim 4, wherein the pressureplate receives the torque inputted thereto from the front cover, and theclutch disc transmits the torque from the pressure plate and the frontcover therethrough to the damper mechanism.
 6. The lock-up device for atorque converter according to claim 1, further comprising: a supportboss having an annular shape, the support boss fixed to an innerperipheral part of the front cover so as to protrude toward the turbine,the support boss for supporting the piston on an outer peripheralsurface thereof such that the piston is slidable in the axial direction;and an oil chamber plate having a disc shape, the oil chamber platefixed to the outer peripheral surface of the support boss such that thepiston is interposed between the front cover and the oil chamber plate,the oil chamber plate for forming a lock-up oil chamber together withthe piston therebetween.
 7. The lock-up device for a torque converteraccording to claim 6, wherein the oil chamber plate includes a torquetransmission part for transmitting the torque from the front covertherethrough to the pressure plate.
 8. The lock-up device for a torqueconverter according to claim 7, wherein the piston includes a pluralityof openings penetrating therethrough in the axial direction, theplurality of openings aligned at predetermined intervals in acircumferential direction, and the torque transmission part isintegrated with the oil chamber plate, the torque transmission partincluded in an outer peripheral part of the oil chamber plate, thetorque transmission part engaged with the pressure plate whilepenetrating the plurality of openings of the piston.
 9. The lock-updevice for a torque converter according to claim 6, wherein the frontcover and the piston form a cancellation oil chamber therebetween so asto cancel a hydraulic pressure to be generated in the lock-up oilchamber in lock-up releasing, and the support boss includes an oilpassage communicated with the lock-up oil chamber and an oil passagecommunicated with the cancellation oil chamber.